void main() {
  // number 类型有2种 int double

  int n1 = 100;
  var n2 = 100;

  double d1 = 3.14;

  print(n1);
  print(n2);
  print(d1);

  var s1 = '100';
  int n3 = int.parse(s1);
  print(n3);

  var s2 = '3.14';
  print(double.parse(s2));

  print(num.parse('100'));

  // false
  print(1.toString() is int);
}
